Method of making sheet material



Jan. 28, 1947- s. P. BOSOMWORTH ETAL 1 ,415,

METHOD OF MAKING SHEET MATERIAL 3 Sheets-Sheet 1 Filed Feb. 9. 1944 awe/WM @EORGIE'. Q $630M WQRTH AND CHARLES K. NOVOTNY 8, 1947. a. P. BOSOMWORTH ETAL. ,0 8

METHOD OF MAKING SHEET MATERIAL 3 Sheets-Sheet 2 Filed Feb. 9, 1944 Qrwwrm GEORGE. P. MSOMWOQTH AND CHARLES K.NOVOTNY Jam 1947- G; P. BOSOMWORTH EI'AL 2,415,028

METHOD OF MAKING SHEET MATERIAL Filed Feb. 9, 1944 3 Sheets-Sheet 3 3|wvwbom GEORGE QDOSOMWRT'H AND CHAQLEJ K. NOVOT NY PatentedJan. 28, 1947 METHOD OF MAKING SHEET MATERIAL George P. Bosomworth, Akron, and Charles K. Novotny, Mansfield, Ohio, assignors to The Firestone Tire & Rubber Company, Akron, Ohio, a corporation of Ohio Application February 9, 1944, Serial No. 521,730

8 Claims.

1 This invention relates to methods of making sheet material, and moreespecially it relates to improved procedure for the manufacture of continuous or long length rubber sheets, either single ply or multi-ply, derived directly from aqueous dispersions of rubber such as latex.

In the manufacture of rubber sheeting of latex by methods that heretofore obtained, it was customary first to produce a sheet of film thickness (.002" to .004"), and subsequently to assemble a number of plies of such film to produce a sheet of the desired thickness. The film was initially formed on a backing structure, either by dipping or spreading, and in some cases was removed from the backing prior to the plyup operation. In no case was it possible to produce single ply sheeting of substantial thickness, say .050".

Among the several products made from latex rubber may be mentioned hospital sheeting (about .015" thickness) and lining material for liquid fuel cells, such as self-sealing gasoline tanks, (about .125" thickness). The hospital sheeting should be non-porous, clear, and have a smooth soft feel. The material for lining fuel tanks should possess the same characteristics, and in addition should be of accurate and uniform gauge.

The chief objects of the invention are to provide accuracy of gauge of the product of the invention; to obviate manual handling and manipulation of the respective plies of the laminated sheet material; to provide in a simple manner for obtaining adequate adhesion of the piles of the laminated sheeting; to provide sheeting that readily may be joined to other like sheeting by a stepped splice; and to provide rubber latex sheeting having a smooth, soft feel. In short, the invention aims to conserve time and labor in the manufacture of latex sheet material of superior quality. Other objects will be manifest as the description proceeds.

Briefly stated, the improved method of making latex sheeting comprises progressively spreading a layer of prepared latex upon an endless backing structure such as a driven conveyor belt, and then subjecting the layer of material on the conveyor progressively to controlled conditions of temperature and humidity to effect the successive gelling, vulcanizing, and drying of the material. The material may be removed from the conveyor after one traverse of the apparatus, or it may remain on the conveyor while the latter makes several traverses of the apparatus, there being an additional layer spread upon the conveyor with each traverse, and gelled, vulcanized, and dried thereon, to produce a laminated structure. The invention also contemplates that a laminated sheet constructed in the manner set forth may be stripped from the conveyor and withheld while a second laminated sheet is constructed thereon. The first-constructed sheet is then progressively fed back onto the conveyor and cohesively united with the laminated sheet last constructed thereon, after which the composite sheet thus formed is progressively removed from the conveyor.

Of the accompanying drawings:

Fig. 1 is a somewhat diagrammatic view, on a greatly reduced scale, of one type of apparatus, adapted for the practice of the invention;

Fig. 2 is a perspective view, on an enlarged scale, of a fragmentary portion of a sheet of material constituting one of the products of the invention;

Fig. 3 is an edge elevation, on an enlarged scale, of a laminated sheet made according to the invention, showing the respective ends of the single sheet of which it is composed;

Fig. 4 is an edge elevation, on an enlarged scale, of a splice at the juncture of the ends or margins of two multi-ply sheets;

Fig. 5 is a diagrammatic detail showing the method of removing laminated sheet material at the right hand end of the apparatus; Fig. 6 is a diagrammatic detail showing showing the feeding back of a sheet of laminated material onto the conveyor having a second sheet of laminated material thereon, and the subsequent removal of the two cohesively united laminated sheets as a unit;

Fig. 7 is a diagrammatic elevational detail, on a larger scale, showing how two laminated sheets are assembled; and

Fig. 8 shows another embodiment of the oven of the apparatus capable of numerous variations in the control of drying conditions, to compensate for variations in the thickness of the sheeting, the type of latex composition employed, and the type of sheeting desired.

Referring now to Fig. 1 of the drawings, there is shown sheet-forming apparatus comprising an endless conveyor belt in thatmay be composed of aluminum or other suitable material, waxed or otherwise treated, to which rubber latex does not strongly adhere, and which will not form blisters on the material deposited thereon. Said conveyor is mounted upon suitable rollers or pulleys II, II, at least one of which is driven so as to impel the conveyor in the direction indicated by the arrows. At one region of its upper reach the conveyor passes over a supporting roller i2, and positioned above the latter and the conveyor thereon is a doctor blade I! that extends transversely of the conveyor and is mounted upon a holder II, the latter being vertically adjustable, from and toward the conveyor, to vary the spacing of the doctor blade from the surface of the conveyor. The holder It also assists in supporting a pair of lateral guard plates, such as the plate II, which plates are disposed adjacent opposite sides of the conveyor it and retain a bank of viscous rubber latex l6 thereon. The bank of latex is constantly supplied with fresh latex by a delivery nozzle ll having connection with a suitable source oi latex (not shown). The arrangement is such that a layer of latex of determinate thickness is spread upon the moving conveyor by the doctor blade ii, at the posterior side of the latter. The foregoing apparatus is shown and described in greater detail in the copending application for Letter Patent of George P. Bosomworth, one of the co-inventors hereof, said application filed concurrently herewith.

Beyond the doctor blade I) both reachespf the conveyor It extend through an oven that is designated as a whole by the numeral 2|, said oven being an elongate structure that encloses the major portion of the conveyor, and located in the medial region thereof, the opposite end portions of the conveyor being exposed. Interiorly the oven is divided into three compartments consisting of a gelling compartment 2i and a vulcanizing compartment 22 through which the upper reach of the conveyor travels, and a drying compartment 23 through which the lower reach of the conveyor travels. Compartments 2i, 22 are separated by a vertical partition 24, and both of said compartments are separated from the lower compartment 23 by a horizontal partition 2!. Suitable slots are provided in the walls of the oven and in the partition 24 to enable the conveyor to pass therethrough. Mounted within gelling compartment 2| are heating coils 26, 26 that are located above and below the conveyor. To eiiect more rapid gelling of latex on the conveyor, electrical heating elements 21 are located immediately outside the gelling compartment and below the conveyor, but sufllciently remote from the doctor blade it so as not to eilect gellation of the latex banked thereagainst. The heating elements 21 are utilized only when thick layers (.050" or more) of latex are on the conveyor.

Located in the vulcanizing compartment 22, at the end thereof remote from the gelling compartment 2i, and above the conveyor III, is a heating unit 2! that is positioned directly below an adjustable air-inlet port 30 in the top of the oven. Beside the heating unit 29 is a blower fan 3| adapted to draw fresh air into the oven, across the heating unit 29, and impel the heated air across a steam spray 32 and toward the opposite end of the compartment the air being moistened or humidified by said steam spray.

Movement of the air is counter to the movement of the conveyor Ill whereby superior heat transfer to the material on the conveyor is achieved. A drain trough 83 is located below the steam spray to prevent condensate from the spray from falling onto the conveyor. Also heating the air within the compartment 22 is a steam-heated platen 34 located immediately below the conveyor ll. Humidiiied air is removed from the vulcanizing compartment through a duct 28 in the top of the oven, remote from the inlet port 80. Air passing through the duct 28 may discharge into the atmosphere, or it may be conducted therefrom through a duct 3' and discharged into the drying compartment 23, near the delivery and of the latter, through a duct 31. the latter also being adapted for the introduction of fresh air into said compartment. The drying compartment also has a vent or air-outlet duct 28 at the end thereof remote from the inlet duct 31, the arrangement being such that air in the compartment moves counter to the movement-oi the conveyor l0 and material thereon for improved heat transfer. A steam-heated platen II is located in the drying compartment beneath the conveyor i0 therein. The slots through which the conveyor l0 enters and leaves the drying compartment 2i are of such small size that the moving air in the vulcanizlng compartment will not pass therethrough in suiilcient quantity to gell the latex in the bank thereof against the doctor blade.

By regulating the temperature and humidity of the oven, and correlating the temperature and humidity with the speed of the conveyor, the composition of the material thereon, and the thickness of said material, it is possible to effect vulcanization and drying of the material to a determinate degree.

If the sheet material to be produced is thin, the conveyor may be run faster than when the material is thicker, or single-ply material is being made, and experience has shown that superior results are achieved when thicker sheet material is produced inlaminated form. Latex sheeting on the conveyor may be removed therefrom at either end of the apparatus, as Presently will be explained, depending upon the nature of the sheet material being produced. As shown in Fig. 1, sheet material may be removed from the conveyor it at the left hand end of the apparatus at a station designated A, and it may be removed from the conveyor at the right hand end of the apparatus at a station designated B. At the left hand end of the apparatus is a station 0 where laminated sheet material previously removed from the conveyor may be fed back thereonto, for a purpose hereinafter more fully explained.

In the practice of the invention with the apparatus described, the conveyor Ill is constantly driven, a bank or pool of rubber latex i6 is established and maintained on the left hand side of the doctor blade It, as viewed in Fig. 1, and the elevation of the latter is adjusted so that a layer or ply 40 of the latex is spread upon the conveyor on the posterior or right hand side of the doctor blade. The layer III is carried by the conveyor in through the oven 20 where it is gelled and vulcanized in the compartments 2| and 22 thereof. Returning through the oven on the lower reach of the conveyor, the layer 40 is dried to the desired degree in the oven-compartment 23, after which it may be stripped from the conveyor at station A if desired. As is best ,shown in Fig. 6, station A comprises a pair of cradle rolls 2, 42 that extend transversely of the conveyor ill, above and closely adjacent the same, which cradle rolls support and peripherally drive a wind-up roll 43 positioned between the same. Suitably joumaled above the conveyor II is a roll 44 of liner 4!, and a guide-roller 40 for the latter. The sheet material removed at stapartly around the second cradle roll 42 which strips it from" the conveyor, the sheetthen being wound upon the wind-uproll 43 with liner 45 withdrawn from the roll 44 thereof. This completes a cycle of operation for the manufacture of vulcanized and dried, single ply, latex rubber sheeting. In stating that the sheeting is dried it will be understoodthat it is dry in a practical sense, although .two or three percent residual moisture may remain therein.

In the manufacture of laminated latex sheeting, the vulcanized and dried sheet 48 is not removed from the conveyor at station A after one traverse of the oven as previously described, but remains on the conveyor. Then as the leading end of the sheet comes back to point of starting, at the doctor blade l3, the. latter is quickly raised to the extent of an additional ply thickness, with the result that a layer of fluent latex is spread upon and added to the ply 48 thereon. The superposed layer is progressively gelled, vulcanized and dried as the conveyor traverses its course through the oven. The operations described are repeated until a laminated sheet or strip 48 of the desired number of plies has been deposited and dried upon the conveyor, after which the laminated sheet may be removed from the conveyor at station A in the manner previously described. In Fig. 2 is shown a laminated sheet 48 consisting of plies of sheet material 40 arranged in five superposed convolutions. Fig. 3 shows how the respective ends of the sheet 48 merge with the adjacent convolutions to produce a composite sheet of uniform thickness throughout. In the manufacture of laminated sheeting in the manner described, superior cohesion of the plies is obtained when the dry convolutions retain a modicum of moisture, for example, from five to eight percent moisture. The oven 20' orthe speed of the conveyor l8 readily may be controlled to produce latex sheet with any desired degree of residual moisture.

In the freshly produced sheet 48, the plies 48 thereof cohere to each other with suflicient tenacity to enable the sheet to be handled as a unit, but the plies are not so tightly joined as to prevent their separation without dimculty. Thus it is possible sever the ends of the respective plies 40 of a heet 48 in stepped relation, and to join them to the complementally stepped ends of a contiguous sheet 48 to produce a stepped butt splice as shown in Fig. 4. Best results are obtained when the laminated sheets retain considerable residual moisture, for'example, about percent.

Due to a number of factors, it is impractica1 to construct laminated sheeting, by the method just described, to greater than a certain limited thickness. When laminated sheeting of greater thickness is desired, a somewhat different method is employed. Assuming that the practical limit of the apparatus is the vulcanizing and drying of a five-ply sheet, then for producing a ten-ply sheet the following procedure would be employed. First, a laminated sheet 48 is produced in exactly the same manner as previously described except that it is removed from the conveyor In at station B at the right hand end of the apparatus. As is best shown in Fig. 5, station B comprises a suitably journaled roll 580i liner 5|, and a wind-up roll 52 that rests upon the conveyor l8 and is peripherally driven thereby to strip the laminated sheet 48 from the conveyor and to wrap it about itself. The wind-up roll 52 also withdraws the liner 5| from the liner roll 58,

so that said liner is interposed between theconvolutions of the sheet 48 toprevent'them from ply soon is absorbed by the other plies 28 of the sheet, so that before subsequent use the entire sheet does not have more than 8 percent residual moisture. This is desirable since the moisture makes the sheet sufllciently tacky to cohere tightly to a second laminated sheet to be assembled therewith.

Thereafter a second laminated sheet is formed on the conveyor II), which sheet is best shown in Figs. 6 and 7 and is designated 55. Sheet 55 is made by the same process as sheet 48 except that it is not removed from the conveyor at station B, with the result that its top ply is exposed to the drying eifect of compartment 23 of the oven. While the laminated sheet 55 is being formed the roll of sheet material 48 and liner 5| is mounted at station C of the apparatus. As shown in- Fig.

6, the apparatus at station C comprises a pressure r011 56 that rests upon the top of conveyor l8, and a pair of crade rolls 51, 51 disposed beneath the conveyor, transversely thereof in spaced relation and parallel to each other. The pressure roll 55 is disposed between the cradle rolls 58 and thus hows the conveyor slightly therebetween, the arrangement providing substantial area of contact between the pressure roll and the material carried by the conveyor, so as frictionally to rotate the pressure roll. Resting upon the latter and peripherally driven thereby is a liner re-wind roll 58. The station also includes a guide roller 58, and journal means for the roll 52 of sheet material 48 and liner 5|.

As soon as the laminated sheet 55 is completely formed on the conveyor, the first produced laminated sheet 48 is fed back onto the conveyor in superposed relation to the sheet 55 thereon. In this operation. sheet 48 and liner 5| are withdrawn from roll 52 and pass over guide rolls 58. Thence they pass between rolls 58 and 56 where liner 5| is wound onto roll 58, sheet 48 passing around pressure roll 58 and being pressed by the latter progressively into superposed relation with the sheet 55 moving with the conveyor. Because Of the tacky condition of sheet 48, due to moisture thereon, it coheres readily with sheet 55, the composite sheet, indicated at 68, Figs. 6 and 7, moving with the conveyor toward station A. Best results are obtained if the sheet 48 is applied to sheet 55 while somewhat warm, a temperature of -100 F. being found satisfactory. At station A the laminated 10-ply sheet 68 is removed from the conveyor and wound in a liner in exactly the same manner as previously described with respect to a single ply of sheet material 48.

It will be obvious that the plying up operation at station C and the work-removing operation at station A may proceed concurrently, and that at the same time a layer of latex may be spread upon the conveyor at the doctor blade i3, the plying up and work-removing operations being completed in one complete traverse of the conveyor. The arrangement results in economy of time and labor and a superior product is produced.

As previously stated, the invention is adapted.

ture of hospital sheeting when a substantiallyv non-heat-sensitized latex is employed such as the following:

Parts Latex (60%) 166 Water 3.3 Zinc oxide dispersion (50%) 6.5 Sulfur dispersion (50%) 3.0 Sodium diethyl dithiocarbamate solution (25%) 4.0 Sodium silicate solution (40%) 3.3

Although this composition does not sell immediately upon entering the oven, the relative thinness of the sheet (about .015) and the surface tension of the composition combine to prevent appreciable spreading and thinning of the sheet at the lateral margins thereof. In the manufacture of rubber sheeting for fuel cells, which comprise a plurality of plies, straight 60% latex generally is used, without the addition of gelling or vulcanizing agents. In such case it is possible to spread a layer of latex as thick as .040" without appreciable thinning at the margins of the layer.

When spreading very thick layers (.050" or more) it is desirable that heat-sensitized latex be employed, and in some cases to utilize the electrical heating elements 21 of the apparatus. Heat-sensitive latex of the following composition has been found to give satisfactory results:

1 Sodium salt of polymerized alkyl-aryl-sulfonic acids.

The invention also is adapted for the manufacture of sheeting of sponge or cellular rubber. In such case the latex is beaten or frothed, after which a gelling agent is added. Because the froth is less fluent than unfrothed latex, it may be spread on the conveyor to greater thickness. Thus it is possible to operate the apparatus with a blade setting of inch to produce sponge sheeting having an ultimate thickness of inch.

Referring now to Fig. 8 of the drawings, there is shown an oven that is somewhat more complex than that shown in Fig. 1, and which is more especially adapted for obtaining the various conditions of temperature and humidity that enable the apparatus to process latex compositions of various characteristics. The oven, which is designated as a whole by the numeral 65, comprises successive gelling compartments 66, 61 and successive vulcanizing compartments 68, 68, and I disposed in the upper portion thereof, and drying compartments II, I2 in the lower portion thereof beneath vulcanizing compartment 68 and Ill respectively, said compartments being separated by suitable vertical and horizontal partitions. The end walls and vertical partitions are suitably slotted to enable the endless conveyor I0 to pass therethrough the upper reach of the conveyor passing through the drying and vulcanizing compartments and the lower reach of the conveyor passing through the dryin compartments.

At the end of vulcanizing compartment 68 remote from gelling compartment 61 is an adjustable fresh-air inlet duct 14, and adjacent the same above the conveyor is a steam-heated coil I5 and a blower fan I6 adapted to draw fresh air through the coil I5 and impel it longitudinally of the compartment, counter to the movement of the conveyor. In front of the blower I6 is a steam spray 'I'I adapted to moisten or humidify the heated air from said blower, there being a drain trough 18 below said spray extending transversely of the conveyor for removing water of condensation, thus preventing the latter from blemishing the sheet material on the conveyor. Moist air from compartment 68 enters gelling compartments 61 and 66 through the slots through which conveyor I0 passes. Moist air is vented from compartments 68 and 66 through branch ducts I9, respectively that connect with a main ventilating duct 8|, said air being withdrawn from the tops of said compartments. There is appreciable space between the conveyor I0 and the bottom of the oven, which space is continuous from compartment 66 through compartment 68, and in said space, below compartments 66, 61 and close to the conveyor is a steam heated platen 82. A similar platen 83 is positioned in said space below compartment 68, and extends about two-thirds the length of the latter. Fresh air may enter said space through an adjustable inlet port 84 in the bottom of the oven, and the cooler humid air may enter said space through openings between said platens and between platen 82 and the end-wall of the oven. The air is drawn through said space by the suction created at the end thereof by the fan 16, said air mixing with fresh air from the port I4 and passing through the heater therewith. The arrangement is such that but little of the heated air in compartment 66 escapes through the conveyor slot in the end wall of the oven, and there is no gelling of the latex in the bank or pool thereof at the doctor blade. The temperature in compartment 68 usually is maintained at 180"- 220 F.

Vulcanizing compartment 68 is essentially similar to compartment 68. At the end thereof remote from the latter it has an adjustable inlet port 86 in its top, and has heating coils 8'I, blower fan 88, and steam spray 88 arranged adjacent thereto. At the end thereof adjacent compartment 68 is a vent duct 80 that is in communication with the main ventilating duct 8|. Another vent duct 8I extends from the top of the compartment downwardly past the drying compartment 'II therebeneath, and has ports 82, 83 discharging into said drying compartment above and below the conveyor I0 therein. Duct 8| has an extension 84 through which fresh air from th atmosphere may be drawn or forced into said compartment II. A battery of steam heated coils 85 are positioned in compartment 68 immediately below the upper reach of conveyor l0 therein. Hot, humid air circulates within com- 9 partment 60 in the same manner as in compartment 00, the temperature in thecompartment usually being maintained at 210-240 F.

Vulcanizing compartment 10 is substantially identical with compartment 69 in the arrangement of its inlet port 91, steam coil 98, blower fan 99, steam spray I00, vent ducts IOI, I02, and steam coils I03. The use of the steam spray .I is optional; for example, it will not be employed in the manufacture of laminated sheeting by the method that requires the sheeting to b removed from the conveyor I0 at station B at the right hand end of the apparatus, withthe result that substantial drying of the uppermost ply of the sheeting will be effected in compartment I0. Usually this compartment is maintained at 220- 260 F.

Drying compartment II, located below compartment 69, has a battery'of heating coils I located therein below conveyor I0. This compartment has an adjustable outlet port I 06 in the bottom wall of the oven, and also has an outlet port consisting of an opening I01 in the horizontal partition constituting the top of the compartment, said opening being disposed directly below inlet port 00 of compartment 69. The arrangement is such that air will be drawn longitudinally of compartment II by the suction of the fan 88, which is effective by reason of said opening I01. The temperature in compartment 1| is maintained at 220-240 F.

Drying compartment 12 is substantially identical with compartment II in the arrangement of its battery of heating coils IIO, adjustable outlet port III, and opening 2 into compartment 10. The, vent pipe I02 from compartment I0 may discharge into compartment I2 through resion II5 through which fresh air may be introduced into the compartment. The temperature in compartment I2 is maintained at 220-240 F. From the foregoing description of the oven it will be apparent that substantially any temperatures and degrees of humidity may be provided in various parts of the oven to suit various vulcanizing and/or drying conditions. Furthermore, the conveyor I0 may be driven at any desired speed, say from 1 to 6 feet a minute, so that the sheet material may remain in the oven for the required duration to produce optimum results.

When the sheet material is made from heatsensitized latex, the latter is substantially gelled on the conveyor by the time the latter has traversed the gelling compartments 66, 01, and is substantially vulcanized by the time the conveyor has traversed the vulcanizing compartments 88, 69 and I0. Preferably the drying conditions of ,f'spective ports H3, H4 located above and below I the conveyor I0, said pipe I02 having an exten- By employing a plurality of vulcanizing compartments it is possible to expose the work to progressively increasing vulcanizing temperatures. Thus from the compartment 68 to compartment 10 the temperature may vary from 180 to 260 F. Preferably the drying compartments II, II are not quite as hot as the vulcanizin compartments. Thus the temperature of the sheet material will gradually increase as-it passes through the oven, and will have a temperature of about 212 F. at the time it leaves the same. Because there is no drying compartment beneath compartments 6G to 60, latex sheeting on the cone veyor will have time to cool between the time it leaves the oven and the time it reaches station C of the apparatus, the temperature at the latter point desirably being '75-95 F. The time required to effect vulcanization of the sheeting may vary from 30 minutes to 60 minutes depending upon the thickness of the sheet and the composition of the latex employed.

The feature of vulcanizing the material in an atmosphere moving counter to the movement of the material makes for improved heat transfer, and expedites the removal of moisture from the material.

From the foregoing it will be apparent that the invention makes it possible to produce continuous latex sheeting of substantial thickness, and which is clear and with a smooth, soft "feel. Furthermore, the laminated sheeting is without grain, and tears, with difficulty, along an irregular line.

Modification may be resorted to without departing from the spirit of the invention or the scope thereof as defined by the appended claims.

What is claimed is:

1. The method of making laminated sheet material which comprises spreading successive superposed layers of fluent latex composition upon a support, and vulcanizing each layer, without completely drying the same, before spreading a succeeding layer thereupon, to effect union of said layers.

2. The method of making laminated sheet material which comprises spreading successive layers of a vulcanizable aqueous dispersion of rubber in the compartments 1|, 12 are so adjusted that the sheet is substantially dry at the time it leaves the same, although some moisture (3% to 10%) may be allowed to remain in the sheet, especially when other layers of latex are to be superposed thereon, since better cohesion of the piles is thereby attained. When relatively thin sheets of material, such as hospital sheeting, are made, non heat-sensitized latex may b employed. In either case, controlled humidity in the vulcanizing sections assures that vulcanization and/or drying will progress from the interior toward the exterior of the sheet, and the formation of fine cracks in the surface of the sheet will be obviated. This is desirable in the vulcanization since it results in the sheeting having a softsmooth feel which is desired.

superposed relation upon a support, and vulcan-' izing each layer and subsequently removing a substantial but not total portion of the water content thereof before the application of a succeeding layer, to effect union of said layers.

3. The method of making laminated sheet material which comprises progressively spreading a vulcanizable aqueous dispersion of rubber longitudinally of an endless support until a plurality of layers of the dispersion are disposed in superposed relation thereon, and applying moist heat progressively to material on the support to effect vulcanization and thereafter applying dry heat to effect substantial but incomplete drying of each layer before the succeeding layer is applied thereover.

4. The method of making laminated sheet material which comprises progressively forming a layer composed of a vulcanizable aqueous dispersion of rubber and feeding said layer in an endless course to produce a multi-ply structure, and applying controlled moist heat at vulcanization temperature to the structure in one region of its course to effect substantial vulcanization of each ply of the structure before the succeeding ply is added thereto.

5. The method of making laminated sheet material which comprises spreading successive superposed layers of viscous vulcanizable composition upon a moving support while processing each layer to vulcanlze the same before adding a succeeding layer thereto, stripping the laminated vulcanized material from the support, repeating the operation to produce a second sheet of laminated vulcanized material upon the support, progressively feeding the first-made sheet back onto the support in superposed relation to the lami nated sheet thereon and bonding it thereto, and then removing the two laminated sheets as a unit from the support.

8. A method as defined in claim 5 including the step of drying each layer of composition after it is vulcanized, the last layer of the first laminated sheet being permitted to retain some moisture to provide adequate cohesion with the second laminated sheet when the latter is applied thereto.

7. The method for the continuous manufacture of non-porous rubber sheeting from a latex composition which comprises the steps of continuously spreading vulcanizable latex composition on a continuously moving surface to form a layer of uniform thickness upon said conveyor, then prior to drying, subjecting the unconfined continuously successive areas of said layer to a hot humid atmosphere to eflect at least partial vulcanization thereof, and thereafter drying the vulcanized latex rubber.

8. The method for the continuous manufacture of non-porous rubber sheeting from a latex composition which'comprises the steps of continuously spreading vulcanizable latex composition on a, continuously moving surface to form a layer of uniform thickness upon said surface, then subjecting the unconfined continuously successive areas of said layer to successive zones of humid atmosphere of progressively increasing temperature to effect at least partial vulcanization thereof and thereafter drying said sheeting.

GEORGE P. BOSOMWOR'I'H. CHARLES K. NOVOI'NY. 

